240 Fuel Pump Relay

[rtbcomp]

Hope this can be of help to some of you.

The following refers to my 240 SE Estate, UK model, it runs on petrol and it's red.

This is the circuit as far as I can tell, my Haynes manual doesn't even resemble what I have on my car.

If I've got anything wrong or left any gaps, please add your comments!

1992 240 SE Fuel Pump Relay 01.jpg

When the ignition is switched on both relays close and power is applied to both pumps (one is in the tank and the other isn't). I'm not sure which pump is fed from which relay.

I'm guessing the ECU controls the relays by providing them with a ground path.

If the engine isn't cranked for about a second (or it stops due to a crash or something) relay 2 drops, switching that pump off.

You can test the circuit with a test lamp as follows:

1) connect one of the test leads to the chassis and the other to the LH end of fuse 6, the lamp should light, if not check the clips, leads and bulb.

2) connect the test lead to the RHS of Fuse 6, if it doesn't light now check the fuse (6), it may have blown or not connecting with its holder correctly. This fuse can run warm which may cause it to distort, weaken the spring connector of the holder or make the contacts corrode.

3) with fuse 6 working move the test lead to the LHS of fuse 4, turn the ignition on (don't try to start the car) and the lamp should light immediately and go out after about a second. If it doesn't light it looks like a faulty relay.

4) if it lights OK repeat the test with the lamp connected to the RHS of fuse 4. If it doesn't light this time give the fuse the same treatment as for fuse 6 above.

5) now you have power to both pumps and if the car still doesn't start something else is wrong.

If you listen carefully you can hear the pumps, they both run for about a second then one of them stops, the other stops when you switch the ignition off.

If you can't hear the pumps it's time to examine the relay.

The relay is fitted to the inside of the bulkhead, behind (or in front really) of the glove box, which has to be removed for access. To do this open the door (of the glovebox) and remove the cross-head screws around the perimeter of the glovebox. Then pull the glovebox towards you, no need to empty it. The little light will remain behind, lit. Pop the light assembly out towards you to extinguish it (this removes its earth).

You can see the relay ahead of you, it's the white plastic thing:-

1992 240 SE Fuel Pump Relay 02.jpg

Simply slide it out of its clip and unplug the connector to remove it.

To remove the cover spread it slightly where it joins the base to release the clips and withdraw the relay complete with its base, you need three hands ideally.

[rtbcomp]

With the relay exposed, press the clapper of each relay in turn and each pump should run. If not and the fuses have been check out there could be a fault with the pump(s) or wiring thereto or there may be a dry joint on the relay circuit board.

If the pumps run OK then you could still have a dry joint or the ECU isn't doing its job.

Dry joints show as ring in the solder around the pin on the solder side of the circuit board, simply melt the solder with a 25 watt iron and add a bit of new flux-cored solder to re-flow the joint. You can use flux without extra solder, but on no account use aggressive plumbing fluxes, use proper electrical flux. Otherwise the joints might corrode, (don't ask how I know).

If the relay still doesn't work then you'll have to fit a new one.

This is a general view showing the relay with its cover off and the glovebox light disconnected. Bear in mind when doing all this that the big bit of exposed copper in the relay is at 12volts, so don't let it touch the bodywork!

1992 240 SE Fuel Pump Relay 03.jpg

[rtbcomp]

If (When) you decide the fuseholder is shot, it is a simple matter to convert to blade fuses, in my case it was fuseholder 4 that was faulty, but I replaced both 4 and 6 at the same time.

The bits you need can be got from these guys http://www.beal.org.uk/

Assuming you've already done the previous steps, you now need to switch the radio off, remove the battery earth and drop down the cover over the passenger's footwell.

To do this last step, turn the three plastic catches along the top edge of the cover through 90 degrees (either way) and gently prise the cover down. You will be met with this sight:

Fusebox 03 Small.jpg

The three relays that fell out are the dim/dip relay (the silver thing) and the front and rear wiper relays.

It makes access to the wires easier if you loosen the fuseholder, just remove the two screws (Torx) and there will be enough slack on the wiring to move the fusebox slightly.

[rtbcomp]

Next, remove the yellow/red wires from fuse 6, thin nosed pliers are useful here. There are three wires, 2 have uninsulated crimps and the third has an insulated connector. The uninsulated ones are connected to the RH end of the fuse (load) and the insulated one is the live feed to the LHS. (See post #1).

Loop these wires back so the ends appear at the opening in the top right of the plastic trim:-

Fusebox 04 Small.jpg

The fuseholders I used are the stacking type and have one connection in and one out, this means the wires to the load have to be joined together in one crimp connector as shown in the photo. The wire to the supply side just plugs onto the fuse using the existing crimp.

I used a 7.5 amp fuse here.

[rtbcomp]

Replacing fuseholder 6 is more involved.

The feed side (LH) to this fuse is commoned to some of the adjacent fuses, so you can't remove the red live feed wire, so this is what you do!

Disconnect the uninsulated wire to the RHS of fuse 6 and loop it out as in the previous post and connect it to one side of the 2nd new fuseholder.

Next you will need a length of 20 amp cable, attach an insulated crimp to one end and tin the other with solder, make a tidy job, we don't want stray strands of wire shorting out. Use flux-cored electrical solder.

Feed the tinned end of the wire through the trim so it reaches fuseholder 6. It would be as well to put an insulating sleeve over the exposed connector.

Next tin the LH contact on the fuseholder. You will need to clean the connector to a bright colour otherwise the solder won't take. I used a small screwdriver to do this. Tin the connector.

Using three hands hold the tinned wire onto the tinned connector, apply heat from the soldering iron and run some more solder into the joint. Hold the joint absolutely still until the solder sets, otherwise you'll end up with a dry joint.

Fusebox 02 Small.jpg

Connect the new wire to the other end of the new Fuse 6 holder. I used a 15 amp fuse in this position.

Fusebox 05 Small.jpg

Now try to start the car, if it doesn't start then reconnect the battery.

It's unlikely anyone would be daft enough to solder the wire to wrong fuseholder, but if the car still doesn't start it would be as well to check.

[Kwekkel]

Great info! Thanks

[rtbcomp]

For completeness this is the wiring diagram for the earlier 240 fuel pump relay

1986 200 Fuel Pump Relay 01.jpg

The bottom box in the relay is a re-triggerable monostable, which means that it energises the relay coil (top box) as long as there is a train of pulses from the coil, i.e. the engine is turning over.

You can see the fuse arrangement is pretty much the same as above so I don't see any reason why a blade-type holder couldn't be fitted.

[rtbcomp]

Originally Posted by rtbcomp

.............

When the ignition is switched on both relays close and power is applied to both pumps (one is in the tank and the other isn't). I'm not sure which pump is fed from which relay.

.........

According to the handbook, fuse 4 (8 amps) feeds the pump in the tank and fuse 6 (16 amps) feeds the main fuel pump.

From what I can see fuse 6 actually feeds both pumps as shown in the circuit in post #1.

According to my handbook, fuse 4 also feeds electrically heated Lambda Sond, Fuse 6 also feeds the injection system, Lambda Sond & ABS.

[cybertrack]

Another possible solution found:

I have a 240 1993 which for the past ten years has had problems with starting failure due to fuel pumps not running. The car usually ran fine, but from time to time it would not start or even stall along the highway - forcing me to jump fuse 4 and 6 to get moving again.

I have spent hours trying to find the source of the problems and made me replace relays, fuel pumps and ecu. The car has always fixed itself before I was able to complete searching and testing.

Well, yesterday the car was finally really dead and I found out that the relay was working fine, the ecu was grounding as it should, yet the car still would not start. There was 12v present at 87/2, but 0.0v at fuse 4. Today I found that the wire going from the relay to fuse 4 is going through a connector placed near the relay, behind the glove box. Inside this connector the y/r wire was burned, obviousoly caused by insfficent contact.

This defect was not easy to see, and I think the location of the connector has caused me to move it a little bit each time I was checking the relay and this movement gave contact again. Still it is not obvious just by loooking at the wire harness that this connector is relvant for the relay.

[slylykafox]

where does the red wire coming out #6 go to? iv found it broken. fixing up previous owners dodgy wiring. iv got 87 240 b230f.